This invention relates to a novel method for vaporizing getter material inside a succession of cathode-ray tubes and particularly, but not exclusively, to a novel method for flashing the getter material from getter containers in each of a succession of color television tubes, which tubes may be of different sizes and/or shapes and may be randomly intermixed.
In one popular design of a color television picture tube, which is a type of cathode-ray tube, a ring-shaped getter container having getter material therein is held against or close to the inner surface of that part of the envelope, called the funnel, which is conical in shape. After the envelope is evacuated of gases and sealed, an induction coil is positioned against or close to the outer surface of the envelope opposite the getter container and is then energized with a high-frequency current. The magnetic field generated by the energized coil induces currents in the getter container causing the temperature of the getter container and the getter material therein to rise rapidly until getter material, which is usually barium metal, vaporizes or "flashes" and deposits as a getter film on internal surfaces of the tube. A purpose of the getter film is to absorb (a) residual gas left in the envelope after evacuation and (b) adsorbed gas that is later evolved from internal surfaces during the operating life of the tube. The life of the tube is determined principally by the ability of the getter film to continue to absorb gas and to maintain a low gas pressure in the envelope.
In order to vaporize the maximum amount of getter material from the container and to realize a desired distribution of deposited getter material in the tube, it is necessary to position the induction coil properly with respect to the getter container so as to produce optimum magnetic coupling between them. This is not easily done. Although the envelope is usually constituted of a transparent glass, the getter container cannot be seen (optically) from outside the tube because the inner surface of the envelope opposite the getter container is coated with an opaque internal coating.
Heretofore, it was the common procedure to make a dummy tube without any opaque internal coating present, and then to determine where the induction coil should be located on tubes of that design in order to flash the getter material from the getter container. For each tube design; that is, for each shape and/or size, the getter container was located at its own unique position with respect to the longitudinal axis of the tube both measured normal to the tube axis (radial distance) and up from some plane normal to the tube axis (axial distance), even though the containers were in a particular longitudinal plane that intersects that longitudinal tube axis. Thus, during factory production, it was necessary from a practical standpoint to process a batch of tubes of the same design, then to reset the induction-coil positioner for the succeeding batch of tubes of a different design. Or, if a randomly intermixed succession of tubes of different designs was processed, it was necessary to recognize the design of each particular tube as it presents itself, to remember its getter position, and to position the induction coil opposite that position. Or, if randomly intermixed, the tubes were sorted by design and then processed in different machines, each of which was set up for a particular tube design.